Magnesium firearm forearm and method of manufacture

ABSTRACT

A forearm for a firearm that includes a magnesium alloy body. The forearm can be adapted for use in a modular rifle having both an upper receiver securable to a barrel and a lower receiver housing a trigger assembly. The magnesium body may also be nickel plated and have a ceramic coating on the nickel plating. Also disclosed are methods of manufacturing a forearm having a magnesium alloy body. The magnesium alloy body may be formed by extrusion or by thixotropic molding. In some embodiments, the magnesium forearm includes an outer sleeve formed out of a magnesium alloy and an inner sleeve formed out of a different material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) of U.S.provisional patent application Ser. No. 61/863,195 filed on Aug. 7, 2013entitled MAGNESIUM GUN PARTS; U.S. provisional application Ser. No.61/846,674 filed on Jul. 16, 2013 entitled EXTRUDED ALUMINUM FIREARMRECIEVER AND METHOD; and U.S. provisional application Ser. No.61/735,254 filed on Dec. 10, 2012 entitled FIREARM RECEIVER AND METHODOF MANUFACTURE, the disclosures of each of which are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to firearms, parts thereof, and methods ofmanufacturing such parts.

2. Description of the Related Art

Firearms generally include three main parts, the barrel through which aprojectile, e.g., a bullet, is fired; the action which includes themoving parts that provide for the loading, firing, ejection of firedcasing, and unloading; and either a stock (shotguns and rifles) or grip(handguns). The receiver houses most, if not all, of the operating partsthat form the action of the firearm. The receiver is often made out ofsteel or aluminum. Under U.S. law, the receiver is generally the legallycontrolled part that is considered to constitute the firearm itself andwhich has a serial number fixed thereon.

Long arms, such as rifles and shotguns, will often have a forearm whichextends forward of the receiver and at least partially surrounds thebarrel. Typically, the forearm provides a location for the user to gripthe firearm with their off-hand. While some forearms are positionedadjacent only the lower portion of the barrel and do not completelyencircle the barrel, it is also known to use a forearm that completelyencircles the barrel and also serves as a barrel shroud. A barrel shroudprotects the user by inhibiting contact between the user and a barrelthat has become heated due to firing of the gun.

The barrel of the gun may either be in contact with the forearm or bepositioned proximate but slightly spaced from the barrel. When thebarrel is not in direct contact with the forearm, it is generallyreferred to as a free floating barrel. Such free floating barrels aretypically secured to the receiver and this attachment point serves astheir sole point of attachment and support. Free floating barrels aregenerally considered to be more accurate than barrels which bear againstthe forearm because it is thought that the pressure exerted on thebarrel by the contact between the barrel and forearm can change slightlyfrom shot-to-shot thereby causing inconsistent bullet flight paths. Afree floating barrel is not subject to such potentially variable contactpressure. The barrel of a firearm is generally attached to the receiverfor both free-floating barrels and barrels which contact the forearm ofthe gun.

While many firearms have a unitary receiver, some have multiplereceivers. For example, one common form of firearm, often referred to asan AR-style rifle, has both an upper and lower receiver which aredetachably secured together. This type of rifle gets its name from theAR-15 originally introduced by Armalite and which was adopted by theU.S. military as the M-16 rifle. The M-16 is a selective fire weaponcapable of both semi-automatic and fully automatic operation. A civilianversion of the M-16 capable only of semi-automatic fire was subsequentlydeveloped by Colt's Manufacturing Company and sold as the Colt AR-15.For AR-style rifles, the lower receiver generally constitutes theserialized component that is legally controlled as a firearm.

AR-style rifles are modular rifles which include an upper receiverassembly having an upper receiver, a bolt carrier, a barrel and aforearm. The forearm of AR-style rifles often takes the form of a barrelshroud and, as a result, is commonly referred to as a handguard. Thelower receiver assembly includes a lower receiver which houses a triggerassembly and has a port for receiving a magazine. A pistol grip andstock can be attached to the lower receiver.

The modular nature of the rifle provides several benefits. For example,it allows the rifle to be easily customized for a particularapplication. The modular nature of the rifle also allows an individualcomponent or one of the sub-assemblies to be easily replaced if theoriginal is damaged or an alternative design is preferred. The manyadvantages provided by AR-style rifles, also known as modern sportingrifles, have resulted in such rifles becoming one of the most popularstyles of firearm produced today.

While conventional firearm designs and manufacturing techniques arecapable of producing satisfactory firearms, improved cost-efficiency inthe manufacture of firearms and design modifications which improve themanufacturability remain desirable.

SUMMARY OF THE INVENTION

The present invention provides a firearm forearm that includes amagnesium alloy body and a method of manufacture. The disclosed forearmsare light weight and allow for the cost-efficient manufacture of theforearms.

The invention comprises, in one embodiment thereof, a firearm thatincludes a receiver operably coupled with a barrel and a forearmsecurable to the firearm wherein the forearm includes a magnesium alloybody.

The magnesium alloy body may advantageously be nickel plated. Anoven-cure ceramic coating can be applied to the nickel plating. In someembodiments, the firearm is a modular rifle wherein the receiverincludes an upper receiver and a lower receiver; the forearm and thebarrel being mountable on the upper receiver and the lower receiverhousing a trigger assembly. The barrel may be a free floating barrelthat is spaced from the forearm.

In some embodiments, the magnesium alloy body forms an outer sleeve andthe forearm further comprises an inner sleeve formed out of anon-magnesium material, the outer sleeve being disposed about andengaged with the inner sleeve. The inner sleeve may include a steelmaterial.

The forearm may be defined by a pair of separable parts whichsubstantially encircle the barrel when secured together. Alternatively,the forearm may be a unitary forearm which substantially encircles thebarrel.

The invention comprises, in another form thereof, a method ofmanufacturing a firearm forearm that includes forming a magnesium alloybody and processing the magnesium alloy body to form at least a portionof the forearm.

In some embodiments, the magnesium alloy body has a layer of nickelplating formed thereon by a nickel plating process and a ceramic coatingis then applied on the layer of nickel plating.

The magnesium alloy body may be formed by thixotropically molding thebody. When thixotropically molding the body, the magnesium alloy bodyadvantageously has a surface roughness, R_(a), that is betweenapproximately 35 microinches and approximately 60 microinches aftermolding and without any post-molding processing to smooth the surface.Alternatively, the step of forming a magnesium alloy body may includeextruding the magnesium alloy body.

In some embodiments, the extruded magnesium alloy body forms a forearmthat substantially encircles the barrel. After extruding the magnesiumalloy body, the body may be cut lengthwise to form two separable partsof the forearm. The two separable parts advantageously have the sameconfiguration.

In some embodiments, the forearm includes an inner sleeve and an outersleeve disposed about the inner sleeve wherein the magnesium alloy bodyforms the outer sleeve of the forearm and a non-magnesium insert isprovided to form the inner sleeve. Advantageously, the magnesium alloybody forming the outer sleeve is formed by extrusion.

The magnesium alloy body may be formed out of an AZ91D magnesium alloy.In some embodiments, the forearm has a configuration which adapts theforearm for use in a modular rifle having both a lower receiver housinga trigger assembly and an upper receiver securable to a barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofan embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a side view of a firearm having a magnesium forearm.

FIG. 2 is another side view of a firearm.

FIG. 3 is view of a firearm broken down into several majorsub-assemblies.

FIG. 4 is an exploded view of a lower receiver and extension assembly,buttstock and grip.

FIG. 5 is a perspective view showing the removal of a two piece forearmfrom a rifle.

FIG. 6 is an exploded view of an upper receiver, barrel and two pieceforearm.

FIG. 7 is a perspective view of a one piece forearm.

FIG. 8 is an exploded perspective view of a forearm with a reinforcinginsert.

FIG. 9 is an end view of a forearm with a reinforcing insert.

FIG. 10 is an exploded end view of a two piece forearm.

FIG. 11 is an exploded perspective detail view of a two piece forearm.

FIG. 12 is a schematic depiction illustrating the molding of a forearm.

FIG. 13 is a schematic depiction illustrating the extruding of aforearm.

FIG. 14 is a perspective view of an extrusion.

FIG. 15 is a cross sectional view of an extrusion die taken along lineA-A of FIG. 16.

FIG. 16 is an end view of an extrusion die.

FIG. 17 is a schematic depiction of a machining center for the machiningof a forearm.

FIG. 18 is a schematic cross section of a portion of a forearm.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates an embodiment of the invention, in one form, theembodiment disclosed below is not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formdisclosed.

DETAILED DESCRIPTION OF THE INVENTION

A firearm 30 having a lower receiver in accordance with the presentinvention is shown in FIGS. 1 and 2. Firearm 30 is an AR-style rifleand, except for the forearm assembly 70, has a conventional design andconstruction which is well-known to those having ordinary skill in theart.

FIG. 3 illustrates firearm 30 with several of the major sub-assembliesbeing disconnected. More specifically, firearm 30 has been broken downto separate the lower receiver and extension assembly 32, the upperreceiver and barrel assembly 34, the bolt and carrier group 36, and thecharging handle 38. These sub-assemblies, e.g., lower receiver andextension assembly 32 and upper receiver and barrel assembly 34, can befurther broken down into still smaller modular assemblies.

FIG. 4 provides an exploded view of the lower receiver and extensionassembly 32. Illustrated in FIG. 4 are helical compression spring 1,buffer assembly 2, hammer assembly 3, sear 4, selector lever 5, helicalcompression spring 6, bolt catch plunger 7, bolt catch 8, spring steelpin 9, magazine catch 10, helical compression spring 11, pin 12, helicalcompression spring 13, magazine catch button 14, pivot pin 15,disconnector 16, trigger assembly 17, screw 18, lock washer 19, grip 20,helical compression spring 21, safety detent 22, grooved pins 23,grooved pin 24, takedown pin 25, stepped spacer 26, buttstock assembly27, self-locking screw 28, receiver extension tube 29 and lower receiver40. The assembly and operation of the parts shown in FIG. 4 will beunderstood by those having ordinary skill in the art.

The upper receiver and barrel assembly 34, which includes a forearm, isshown in greater detail in FIGS. 5 and 6. The illustrated forearms areadapted for use with AR style rifles and also function as a heat shieldand as a handguard, however, alternative embodiments can be employedwith other firearms. The terms handguard and forearm are usedinterchangeably herein.

The forearm assembly shown in FIGS. 5 and 6 is a two-piece assembly 70 ahaving a pair of separable parts 72 a that encircle the barrel. FIG. 5illustrates the removal from rifle 30 of one of the two handguards 72 athat form forearm 70 a. FIG. 6 is a view of upper receiver and barrelassembly 34 with the handguard assembly 70 a detached from assembly 34.Assembly 34 includes the upper receiver 33 which is secured to barrel35. A slip ring assembly 64 is mounted proximate the attachment ofbarrel 35 to upper receiver 33 and a front sight assembly 66 is mountedon barrel 35 near muzzle 68.

Handguards 72 a are removed from rifle 30 by pressing slip ring 64toward upper receiver 33 and away from front sight 66. Slip ring 64 isbiased toward muzzle 68 and front sight 66 by a spring (not shown). Slipring 64 surrounds a reduced diameter collar 74 on handguards 72 a. Afterdepressing slip ring 64, one of the handguards 72 a can be removed bypivoting the released end of the handguard 72 a away from barrel 35 anddisengaging handguard 72 a from handguard cap 76. Handguards 72 a mayhave retaining tabs (not shown) which fit within openings or recesses incap 76 or otherwise engage cap 76 to thereby secure the muzzle end ofhandguard assembly 70 a. FIG. 5 illustrates one person pressing down onslip ring 64 and a second person removing a handguard 72 a, however, itis will generally be possible for a single individual to removehandguard assembly 70 a without assistance. To attach the handguards 72a, the process is reversed.

Alternative method of attaching the forearm may also be employed. Forexample, the forearm could be provided with helical threads for securelyengaging the firearm or a groove which receives a retractableprojection. In still other embodiments, the forearm could be providedwith apertures through which fasteners are extended to secure theforearm to the firearm. Other suitable methods of securing the forearmto the firearm may also be employed.

As can be understood with reference to FIGS. 5 and 6, handguard assembly70 a substantially encircles barrel 35 with each of the two similarlyconfigured handguards 72 a engaging each other along surfaces 80 thatextend along the length of barrel 35. Vent openings 78 in handguards 72a allow air to escape and thereby dissipate heat from the space betweenbarrel 35 and handguard assembly 70 a.

It is noted that the handguard assembly 70 a depicted in FIGS. 5 and 6has a slightly tapered configuration wherein the diameter of thehandguard assembly 70 a is largest near upper receiver 33 (excludingcollar 74) and becomes progressively smaller toward cap 76. In thisregard, it is also noted that the handguard assembly 70 shown in FIGS. 1and 2 also has a tapered shape. The handguard assembly of FIGS. 1 and 2differs from the assembly of FIGS. 5 and 6 by having an exterior surfacewith a plurality of recesses while the assembly of FIGS. 5 and 6 has agenerally smooth exterior surface. The recesses on the assembly of FIGS.1 and 2 enhance the ability of the user to securely grip the forearm.

The handguard assemblies illustrated in FIGS. 3, 7, 8, 9, 10 and 11 arenot tapered and have a more cylindrical configuration. It is furthernoted that while the handguard assembly of FIGS. 5 and 6 are two piecehandguards, the handguard assemblies of FIGS. 7, 8 and 9 are unitaryhandguards. The unitary handguard assemblies have a tubular form andmust be slid into place either before barrel 62 is attached to upperreceiver 60 or before the front sight assembly 66 is mounted on barrel62 (if a front sight assembly is being used). The mounting of thehandguard assembly on the rifle, whether a two piece or unitary design,will depend on the particular details of the rifle design as will bewell-understood by a person having ordinary skill in the art.

Handguard assembly 70 b shown in FIG. 7 is a unitary handguard and has aplurality of vent openings 86 formed therein. Handguard 70 b alsoincludes an interior threaded portion (not shown) for securing handguard70 b to upper receiver 60. Lugs 88 may be used to secure a bipod orother device to handguard 70 b. The interior threads are located at thesame end as lugs 88. Handguard 70 b also includes four sections of amounting rail such as a Picatinny rail. In the embodiment of FIG. 7, thetop and bottom sections 82 a, 82 b extend for substantially the entirelength of handguard 70 b while the side sections 82 c extend only aportion of the length.

Mounting rails 82 a-82 c provide a standardized mounting feature forattaching accessories, such as a scope or light source, to the forearm.Picatinny rails are one of the more common types of mounting rail andare also known as MIL-STD-1913 rails and have generally T-shaped crosssection with a series of spaced slots 84. Those having ordinary skill inthe art will recognize that the shape of such rails has beenstandardized to allow for the attachment of a wide variety of differentaccessories and that the use of such rails on the forearm of an AR stylerifle and other firearms is a common and known practice.

FIGS. 8 and 9 illustrate a variant of FIG. 7. The embodiment illustratedin FIG. 7 is a unitary handguard that is made entirely out of magnesium.The handguard assembly 70 c illustrated in FIGS. 8 and 9 has a magnesiumouter sleeve 85 and an inner reinforcing sleeve 83 which is formed outof a stronger material. For example, inner sleeve 83 may be a steel oraluminum tube. In this regard, it is noted that some magnesium alloyshave a greater strength than others. The embodiment illustrated in FIG.7, for example, can be manufactured using an AZ91B magnesium alloywithout the use of a reinforcing tube. Other magnesium alloys, AZ91D,for example, do not have physical properties which are identical toAZ91B and may require a reinforcing sleeve 83. The need for areinforcing sleeve is dependent not only on the material used to formthe outer sleeve but also on the dimensions and configuration of theforearm. Not all forearms using an AZ91D alloy will necessarily requirethe use of reinforcing sleeve nor will all forearms using an AZ91B alloynecessarily be sufficiently strong without an insert. Moreover, it maybe desirable to provide additional strength to the forearm through theuse of a reinforcing sleeve 83 even if the material used to form theouter sleeve would be strong enough without such a sleeve.

When using a reinforcing sleeve 83, the outer radial surface 83 a ofreinforcing sleeve 83 contacts the inner radial surface 85 a of outersleeve 85 over a substantial portion of the surfaces 83 a, 85 a whichface each other. The illustrated embodiment includes an inner sleeve 83with vent openings 86a which align with the vent openings 86 of outersleeve 85. The illustrated inner sleeve 83 and outer sleeve 85 also havethe same length. Alternative embodiments, however, may employ differentarrangements of the inner and outer sleeve. For example, the outersleeve could include vent openings that expose a portion of the innersleeve or the two sleeves could have differing lengths. It may also bedesirable in some embodiments for the inner sleeve to have more openingsthan the outer sleeve to reduce the weight of the inner sleeve whilestill providing the desired reinforcing strength or the inner sleevemight not include any vent openings. Although the two sleeves could beslidingly engaged and not fixed together, it will generally be desirableto permanently secure the two sleeves 83, 85 together. The two sleeves83, 85 can be secured together using welds, a press-fit engagement, orother appropriate method.

FIGS. 10 and 11 illustrate another variant of the forearm of FIG. 7. Theembodiment of FIGS. 9 and 10 is formed by taking the forearm of FIG. 7and cutting it in half to form a two piece handguard assembly 70 dhaving a pair of separable parts 72 d that encircle the barrel whensecured together. Each of the two resulting handguards 72 d haveengagement surfaces 90 which abut with surfaces 90 of the opposinghandguard 72 d when the two handguards 72 d are secured about a barrel35. The two handguards 72 d can be secured together using variousmethods known in the art such that described above with regard to theembodiment of FIGS. 5 and 6. The embodiment of FIGS. 9 and 10, however,use threaded fasteners. As seen in FIG. 10, an access area 96 and anaperture 98 are cut in the handguards 72 d and threaded fasteners 92 areengaged with nuts 94 to secure the two handguards 72 d together to formhandguard assembly 70 d, for example, four sets of fasteners 92 and nuts94 can be used to secure the handguards 72 d. It is also noted thatinstead of using a loose nut 94, threaded inserts could be embedded inone of the handguards 72 d to engage threaded fasteners 92.

A variety of other modifications can also be made to the illustratedhandguard assemblies. For example, AR style rifles originally all used agas impingement system to cycle the spent shell casing and load a newround into the chamber. In a gas impingement system, propellant gasesare bled from a port in the barrel into a tube which conveys thepressurized gas to a location where it can impinge upon the bolt carrierand perform the cycling operation. In recent years, a number ofmanufacturers have begun manufacturing AR style rifles with a gas pistonsystem. In this alternative, pressurized gases are bled from the barrelthrough a port and impinge upon a piston. A rod connected to the pistonis used to impinge upon the bolt carrier. In gas piston systems, the hotand dirty propellant gases are not introduced into the receiver tothereby reduce fouling of the action of the firearm. Because the tubeconveying the gases or the piston and rod assembly acted upon by thepropellant gases is typically located alongside barrel 35 for AR stylefirearms, the configuration of the handguard assembly will often beinfluenced by whether the firearm is using a gas impingement or gaspiston system. Various configurations of handguards suitable for usewith gas impingement systems and gas piston systems are well known tothose having ordinary skill in the art and can be employed withalternative embodiments of the present invention.

The illustrated handguards can be formed by injection molding athixotropic, semisolid magnesium alloy and subsequently applying anickel coating using an electroless nickel plating process. In thisregard, it is noted that handguards for AR-style rifles are mostcommonly formed out of aluminum or plastic. Magnesium is lighter thanaluminum and comparable in strength. For example, lightweight magnesiumalloys may be 35% lighter than aluminum alloys. Although plastic islighter than magnesium, magnesium is significantly stronger.

As mentioned above, magnesium alloys such as AZ91B and AZ91D can be usedwhen molding the illustrated handguards. The composition of an AZ91Bmagnesium ally may include by weight 8.3 to 9.7% Al, 0.13% Mn min., 0.35to 1.0% Zn, 0.50% Si max., 0.35% Cu max, 0.03% Ni max, and 0.30% maxother (total) with Mg forming the balance of the alloy. The compositionof an AZ91D magnesium alloy may include by weight 8.5-9.5% Al,0.45-0.90% Zn, 0.17-0.4% Mn, ≦0.05% Si, ≦0.025% Cu, ≦0.001% Ni, and≦0.004% Fe with Mg forming the balance of the alloy. Magnesium alloyssuch as AZ91B and AZ91D are commercially available and well-known tothose having ordinary skill in the art.

The use of a thixotropic injection molding process to form handguardassemblies 70 a-70 d is schematically depicted in FIG. 12. Moldingmachine 100 includes a supply system 102 for feeding magnesium chips andan inert gas supply 104. The introduction of an inert gas such as argonprevents the magnesium from igniting. The magnesium chips and inert gasare fed into an injector barrel housing a screw 106. Heating elements108 heat the content of the barrel. Heating elements 108 partially meltthe magnesium chips while screw 106 provides the shearing forcenecessary to create a thixotropic slurry out of the semi-moltenmagnesium. Injector mechanism and accumulator 110 accumulate and thenforce the thixotropic magnesium into mold 112 under high pressure. Afterallowing the magnesium to cool within mold 112, the mold is opened toremove the forearm.

Thixotropic injection molding typically provides a laminar melt flow ata relatively low temperature which provides for quick cooling withlimited shrinkage and high dimensional accuracy. Thixotropic injectionmolding also typically results in relatively high densities and lowporosity. The dimensional stability and tight tolerances obtainable bythixotropic injection molding is result of several factors includinglaminar flow of the thixotropic slurry into the mold, the high pressuresused when filling the mold and rapid solidification. The highdimensional stability, tight tolerances and low draft obtainable bythixotropic injection molding of a magnesium alloy allows for themolding of complex geometries.

The molded handguards also have a semi-smooth surface. After molding,and without any post-molding processing, it is possible to obtain asurface having a surface roughness, R_(a), of approximately 35microinches to approximately 60 microinches (approximately 0.00089 mm toapproximately 0.0015 mm) when thixotropically molding a magnesium alloy.The semi-smooth skin and ability to mold complex geometries held totight tolerances, allow handguards to be molded with preformed openingsand other design features that might otherwise require significantmachining to form. Furthermore, for those features that are machined,magnesium is a relatively easy material to machine.

Minimizing the machining of the handguards is advantageous not only forreasons of manufacturing efficiency but also because it reduces thesmall particles of magnesium that are generated during the machiningprocess. Small particles of magnesium are relatively easily ignited andthus must be carefully handled. Minimizing the volume of such particlesis advantageous.

In the illustrated embodiments, it is noted that the general structureof Picatinny rails 82 a-82 c can be formed by the molding operation withPicatinny rail slots 84 and other engagement surfaces of the Picatinnyrails 82 a-82 c being machined after the molding operation. It may alsobe advantageous to roughly mold slots 84 in rails 82 a-82 c and clean upthe surfaces with post-molding machining operations. While it may alsobe possible to form rails 82 a-82 c by the molding operation alone andwithout any post-mold machining, it will generally be desirable tomachine the engagement surfaces of rails 82 a-82 c to obtain tightlycontrolled tolerances. Vent openings in the handguards areadvantageously formed by molding but could alternatively be subject tolimited post-molding machining or formed entirely by post-moldingmachining operations.

FIG. 17 schematically depicts a CNC machining center 184 that can beused to machine the magnesium alloy bodies forming the handguards toachieve the desired final shape. The illustrated CNC machining center184 includes a workbed 186. A carriage 188 allows tooling 190 to berepositioned relative to workbed 186. A controller 192 controls theoperation of the tooling 190. Various other machining equipment known inthe art can also be used when machining the handguard assemblies.

After molding and machining the handguard, it is tumbled in a ceramicmedia for deburring, then cleaned and plated. Either an electroplatingor electroless plating process can be used to plate the handguard.Plating the magnesium body protects the magnesium from corrosion,notably galvanic corrosion.

Although electroplating can be employed, an electroless nickel platingprocess provides several advantages. Electroless nickel plating is anauto-catalytic chemical process that deposits a nickel-phosphorus layeron the magnesium components of the handguards. In an electroless nickelplating process, a reducing agent is used to react with metal ions todeposit metal on the object being plated. In the illustrated example, alayer of nickel is deposited on the handguards. Unlike electroplating,electroless nickel plating does not require the use of an electricalcurrent to form a deposit on the work piece. The absence of flux-densityand power supply variations allows the electroless nickel platingprocess to provide a more even deposit on complex geometry than would anelectroplating process. The use of an electroless nickel plating processalso provides the handguard with a more durable coating than would aconventional ion-exchange chromating process.

Once plated, the handguard can be assembled in a firearm 30. If thehandguard will be combined with an inner sleeve, the inner sleeve andouter magnesium sleeve will be combined before installing on the firearm30. The electroless nickel plating also allows for the application ofone or more additional layers of material such as those applied tofirearm components made out of traditional materials. For example,another layer of plated material using traditional plating methods couldbe applied to the electroless nickel plating layer. Alternatively, itmay be desired to apply a camouflage pattern to the handguard. Materialsand methods of applying camouflage patterns to firearms is well-known inthe art.

An oven-cure ceramic coating can be applied to the nickel plating toprovide it with the desired color and/or camouflage pattern as well asenhance the wear and weather resistance of the forearm. For example, aCerakote™ coating commercially available from NIC Industries, Inc.located in White City, Oreg. can be applied over the electroless nickelplating layer and form the exterior layer of the handguards. Theapplication of various other material layers to enhance the appearance,wear or weather resistance of a firearm that can be applied to a nickelplated surface using traditional methods are also well known to thosehaving ordinary skill in the art.

FIG. 18 schematically depicts a cross section of a portion of a forearmand the thickness of layers 122 and 124 is exaggerated for purposes ofgraphical clarity. As can be seen in FIG. 18, a magnesium alloy body 120forms the structure of the illustrated portion of the forearm and has alayer of plating 122 deposited thereon. In the illustrated embodimentplating layer 122 is a layer of nickel plating. Deposited on top ofplating 122 is a layer of ceramic coating 124. In the illustratedembodiment, both the plating layer 122 and ceramic coating 124 areapplied to all surfaces of the magnesium alloy body 120. It willgenerally be desirable to apply a plating layer 122 to all surfaces ofthe magnesium body 120. Ceramic coating 124 can also be advantageouslyapplied to all external surfaces of the magnesium body as exemplified inthe illustrated embodiment. In some embodiments, however, it may bedesirable to be more selective as to which surfaces receive plating 122and ceramic coating 124. For example, it may be desirable to omit eitherplating 122 or coating 124 from the inner surface of a magnesium alloybody forming the outer sleeve of a forearm that receives an innersleeve.

Turning now to FIGS. 13-16, another method of manufacturing ahandguard/forearm will be discussed. The method illustrated by FIGS.13-16 involves the extrusion of the forearm. FIG. 13 schematicallydepicts an extruder 170 that can be used to form an extrusion having theshape of unfinished forearm 162 in FIG. 14. Extruder 170 includes ahydraulic press 171 which powers a ram 172. Ram 172 extends intocontainer 174 which holds a billet 176 of the material to be extruded. Adummy block, not shown, is placed between billet 176 and ram 172. A die180 is installed at the end of container 174 opposite ram 172. Controls178 govern the operation of extruder 170. As ram 712 is extended, billet176 is forced through die 180 to form an extrusion with theconfiguration of unfinished forearm 162.

When using an extruder, the billet may either be cold or heated. In acold extrusion process, the billet is placed in the container in a solidform at ambient temperature. Alternatively, the billet may be heatedbefore it is placed in the container. In a hot extrusion process, thebillet is heated to a temperature above the recrystallizationtemperature of the material. In a warm extrusion process, the billet isheated to a temperature above the ambient temperature but below therecrystallization temperature of the material.

Although magnesium alloys can be cold extruded, when forming an extrudedforearm a warm or hot extrusion process is advantageously employed. Forexample, the billet may be an AZ91D magnesium alloy. The composition ofAZ91D magnesium alloys is known in the art and typically includes about8.5-9.5% Al, 0.45-0.90% Zn, 0.17-0.4% Mn, ≦0.05% Si, ≦0.025% Cu, ≦0.001%Ni, and ≦0.004% Fe with Mg forming the balance of the alloy. This alloyhas high strength and good corrosion resistance and is often used forthe housings of electric appliances.

FIG. 14 illustrates an unfinished forearm 162 that can produced byextruder 170. As can be seen in this figure, unfinished forearm 162defines an axially extending centerline 164. Unfinished forearm 162 hasa cylindrical section 165 that extends parallel with and concentricallyabout centerline 164. T-shaped projections 166 extend outwardly fromcylindrical portion 165 and will define a mounting rail such as aPicatinny rail in the finished forearm. Cylindrical section 165 alsodefines an axially extending center bore through which barrel 35 willextend when the forearm is mounted on a firearm 30.

When forming an extrusion with extruder 170, the extrusion may have anaxial length parallel with centerline 164 that is equivalent to orslightly longer than a single forearm by selecting an appropriatelysized billet 176. Advantageously, a larger billet 176 is used and theextrusion has an axial length that is longer than a single forearm andequivalent to or slightly longer than a whole number of individualforearms whereby the extrusion can be cut transverse to centerline 164to thereby form a plurality of forearms from a single extrusion. Each ofthe individual unfinished forearms 162 can then be machined to form afinished forearm. The use of a billet having a size sufficient to formseveral forearms from a single extrusion will generally providemanufacturing efficiencies over the use of a billet sufficient only fora single forearm.

As depicted in FIG. 14, unfinished forearm 162 has a bore 168 formedtherein during the extrusion process. FIGS. 15 and 16 schematicallydepict a die 180 which can be used to form an extrusion having a boreextending therethrough. As is known in the art, a mandrel can be used toform a centrally located opening in an extrusion. The illustrated die180, includes a mandrel 194 having support legs 196 and a leading edge198. The billet first contacts leading edge 198 and is pierced thereby.The support legs 196 support center die 200 which forms center bore 168.Support legs 196 are located only proximate the leading edge of die 180and allow the material to reform within die 180 after passing by legs196. Depending upon the precise parameters of the extrusion process, thefinished extrusion may include weld lines at the location of legs 196 asa result of the extrusion process. Once the extrusion is formed and hascooled, it is cut to length to form a plurality of unfinished forearms162.

After forming unfinished forearm 162, it is machined to form a forearmhaving the desired configuration similar to the machining of a moldedhandguard. FIG. 17 schematically depicts a CNC machining center 184 thatcan be used to machine an unfinished forearm 162 to its desired finalshape.

When forming the embodiment of FIGS. 10 and 11, unfinished forearm 162is cut in half parallel with center line 164. The general structure ofmounting rails 82 a-82 c are formed by the extrusion process with slots84 and other engagement surfaces of mounting rails 82 a-82 c beingmachined to meet final tolerances after the extrusion operation.

After machining the extruded forearm, it is tumbled in a ceramic mediafor deburring, then cleaned and provided with a surface finish in samemanner as a molded forearm as discussed above. Once the surface of theforearm has been given the desired finish, the forearm is completed canbe assembled in a firearm 30.

Extruded and molded forearms will generally be machined and finished inthe same manner. The configuration of the forearm, however, may make itmore suitable for one process or the other. For example, taperedforearms, such as 70, 70 a shown in FIGS. 1, 2, 5 and 6, are more easilymolded while forearms having a cross section, taken transverse tocenterline 64, that remains relatively constant over the axial length ofthe forearm, such as those shown in FIGS. 3, 7-10 and 14, are moresuitable for extrusion.

In this regard, it is noted that both types of forearms can be formedusing either process. However, if a tapered forearm is extruded, asubstantially amount of material would have to be removed by machiningthereby significantly impacting the efficiency of the process. Themolding of a tubular forearm well suited for extrusion would not presentundue inefficiencies, however, even greater efficiencies will generallybe obtainable by extruding such forearms.

For both molding and extrusion processes, the unfinished forearmresulting from the molding or extrusion process reduces the amount ofmachining required and will generally give the forearm its finalprofile. The forearm is then machined to meet the desired finaltolercances. After the machining, the forearm is plated using anelectroplating or electroless plating process to protect the magnesiummaterial from corrosion such as galvanic corrosion. The plating layercan function as the final finish layer of the forearm or a surfacefinish, such as an oven-baked ceramic coating, can be applied over theplating layer to give the product its final finish and color.

It is noted that the finished forearm may be used in the assembly of anew firearm 30 or be supplied as an aftermarket part. When supplied asan aftermarket part, the forearm allows owners of pre-existing firearms30 to remove the original forearm, such as an aluminum or plasticforearm, and replace it with a forearm in accordance with the presentdisclosure.

While the present invention has been illustrated and described in thecontext of a handguard/forearm for an AR-style rifle, the presentinvention may be utilized with other firearm components, such as scoperings, butt stocks, grips and the like and with firearm components forother styles of firearms. The invention is not limited to the exemplarydesign described herein and the present invention may be furthermodified within the spirit and scope of this disclosure. Thisapplication is therefore intended to cover any variations, uses, oradaptations of the invention using its general principles.

What is claimed is:
 1. A firearm comprising: a receiver operably coupled with a barrel; and a forearm securable to the firearm and comprising a magnesium alloy body.
 2. The firearm of claim 1 wherein the firearm is a modular rifle and wherein the receiver comprises an upper receiver and a lower receiver; the forearm and the barrel being mountable on the upper receiver and the lower receiver housing a trigger assembly.
 3. The firearm of claim 1 wherein the magnesium alloy body has a layer of nickel plating applied thereto and a ceramic coating is applied over the layer of nickel plating.
 4. The firearm of claim 1 wherein the magnesium alloy body forms an outer sleeve and the forearm further comprises an inner sleeve formed out of a non-magnesium material, the outer sleeve being disposed about and engaged with the inner sleeve.
 5. The firearm of claim 4 wherein the inner sleeve comprises a steel material.
 6. The firearm of claim 4 wherein the firearm is a modular rifle wherein the receiver comprises an upper receiver and a lower receiver; the lower receiver housing a trigger assembly and the forearm and the barrel are mountable on the upper receiver.
 7. The firearm of claim 1 wherein the forearm is defined by a pair of separable parts which substantially encircle the barrel when secured together.
 8. The firearm of claim 1 wherein the forearm is a unitary forearm which substantially encircles the barrel.
 9. A method of manufacturing a firearm forearm comprising: forming a magnesium alloy body; and processing the magnesium alloy body to form at least a portion of the forearm.
 10. The method of claim 9 further comprising the steps of plating the magnesium alloy body to form a layer of nickel plating on the magnesium alloy body and applying a ceramic coating on the layer of nickel plating.
 11. The method of claim 9 wherein the step of forming a magnesium alloy body comprises thixotropically molding the magnesium alloy body.
 12. The method of claim 11 wherein the magnesium alloy body has a surface roughness, R_(a), that is between approximately 35 microinches and approximately 60 microinches after molding and without any post-molding processing to smooth the surface.
 13. The method of claim 9 wherein the step of forming a magnesium alloy body comprises extruding the magnesium alloy body.
 14. The method of claim 13 wherein the magnesium alloy body forms a forearm that substantially encircles the barrel.
 15. The method of claim 14 further comprising cutting the magnesium alloy body lengthwise to form two separable parts of the forearm.
 16. The method of claim 15 wherein the two separable parts have the same configuration.
 17. The method of claim 13 wherein the forearm includes an inner sleeve and an outer sleeve disposed about the inner sleeve and wherein the magnesium alloy body forms the outer sleeve of the forearm and the method further comprises providing a non-magnesium insert to form the inner sleeve.
 18. The method of claim 9 wherein the forearm includes an inner sleeve and an outer sleeve disposed about the inner sleeve and wherein the magnesium alloy body forms the outer sleeve of the forearm and the method further comprises providing a non-magnesium insert to form the inner sleeve.
 19. The method of claim 9 wherein the magnesium alloy body is formed out of an AZ91D magnesium alloy.
 20. The method of claim 9 wherein the forearm has a configuration which adapts the forearm for use in a modular rifle having both a lower receiver housing a trigger assembly and an upper receiver securable to a barrel. 